High-strength solid wheels and tires for railroad traction vehicles and cars

ABSTRACT

A steel for high-strength solid wheels and tires for railroad traction vehicles and cars that is more tenacious at the strengths typical of existing steels, and that is less likely to fracture even at constant braking. The steel has a specific ratio between major, alloying and companion elements, so that the steel is of high purity and uniformity. The heat treatment ensures a structure of excellent tenacity at high strength and of special endurance.

BACKGROUND OF THE INVENTION

The present invention concerns high-strength solid wheels and tires offorged and rolled alloyed steel, quenched and tempered, for railroadtraction vehicles and cars.

Solid wheels and tires for railroad vehicles have previously been madeof steel containing 0.48 to 0.52% carbon and 0.75 to 0.80% manganese asdetermined in accordance with UIC Code 812-3/V, 5th edition, Jan. 1,1984.

The most practical steel is steel R7. Its tensile strength (Rm) is 820to 940 N/mm², its break elongation (A₅) at least 14%, and itsnotch-impact work at least 15 Nm in ISO U sections. All these levels arefor 20° C. (room temperature).

Steel R7 is preferably employed for block-braked solid wheels in carswith high axle loads.

From known wheel fractures and from the research into their etiologiesconducted on specific steels it has been concluded that one cause ofUIC-Code steel breakage is insufficient tenacity.

High-speed trains are also equipped with wheels of UIC Code 812-3/VSteel R7. More rigid specifications deriving from heavier axle loads,higher speeds, and greater braking forces, especially in conjunctionwith the constant braking that occurs in mountainous regions, can alsolead to wheel fracture.

SUMMARY OF THE INVENTION

The object of the present invention is accordingly a steel forhigh-strength solid wheels and tires for railroad traction vehicles andcars that will be much more tenacious at the strengths typical ofexisting steels, R7 for example, and that will be less likely tofracture even at constant braking.

This object is attained in accordance with the present invention asrecited in the claims.

A steel with a specific ratio between major, alloying, and companionelements will be a steel of high purity and uniformity. Furthermore, theheat treatment in accordance with the present invention ensures astructure of excellent tenacity at high strength and of especiallyendurance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention accordingly concerns specifying an innovative material forsolid wheels and tires for railroad vehicles along with a heat treatmentfor solid wheels and tires of that material.

Compositions are provided with specific ratios of carbon to chromium tonickel, with specific upper thresholds of silicon, and with particularlylow upper thresholds of phosphorus and sulfur that will subsequent toquenching and tempering yield steels for solid wheels and tires withstrengths equal to or surpassing those of the Steel R7 predominantlyemployed today and with on the other hand far superior tenacities,especially break tenacities. These compositions are as follows:

    ______________________________________                                        carbon:        0.380-0.420                                                    silicon:       ≦0.250                                                  manganese:     0.400-0.600                                                    phosphorus:    ≦0.012                                                  sulfur:        ≦0.005                                                  chromium:      1.000-1.500                                                    molybdenum:    0.300-0.600                                                    nickel:        0.700-1.200                                                    aluminum:      0.015-0.040                                                    nitrogen       ≦0.008.                                                 ______________________________________                                    

In the preceding composition of the steel, the ranges of chromium,molybdenum, and nickel can, furthermore, be changed to the following, inpercent by mass:

    ______________________________________                                        chromium:      1.00-1.30                                                      molybdenum:    0.30-0.50                                                      nickel:        0.70-1.00.                                                     ______________________________________                                    

Temperatures and cooling procedures are provided for quenching andtempering that will ensure such superior tenacities and provide thewheels and tires with minimal strengths similar to those specified inthe UIC Code 812-3/V for Steel R7. These temperatures and coolingprocedures are as follows:

hardening at 850° to 900° C. followed by quenching in water or oil atroom temperature at approximately 20° C.;

and

annealing at 600° to 680° C. followed by slow cooling in air to roomtemperature at approximately 20° C.

The tenacities of the ferrite-perlite carbon-manganese steels previouslyknown from UIC Code 812-3/V cannot be much improved. Steel compositionaccordingly needs thoroughgoing revision, with due attention of courseto purity, homogeneity, and maximal isotropy. Acceptable breaktenacities accordingly necessitate, in departure from theferrite-perlites while retaining the minimal requisite tensile-strengthlevels, a steel of good quenching and tempering all the way through witha fine crystalline and homogeneous quench structure. Specificproportions of stable carbides have a positive effect on sensitivity toburning. The desired long-term rolling strength and resistance tofatigue can be attained with the right combination of structure,strength, and tenacity. This can be derived from the chemistry of thepresent invention and from its specially associated heat treatment.

As much as 1.50% chromium, 0.60% molybdenum, and 1.20% nickel by masscan be tolerated in the alloy.

The sequence of quenching followed by tempering is basically known. Inparticular, it improves tenacities at specific strengths. The particularheat treatment of the wheels and tires also contributes to roll-outproperties, fatigue resistance, and to resistance to burning on the partof the finished wheel and tire. Attention must accordingly be paid toensuring high enough temperatures in the homogeneous gamma mixed-crystalphase, to precipitous chilling, preferably in water, from hardeningtemperature, and to subsequent heating to relatively high annealingtemperatures. The following specifications should be adhered to.

Hardening at 850° to 950° C. followed by quenching in water or oil atroom temperature (approximately 20° C.)

and

annealing at 600° to 680° C. followed by slow cooling in air to roomtemperature (approximately 20° C.).

Since determining the precise heat-treatment parameters for eachspecific case must also take the dimensions of the component intoaccount, the foregoing figures may vary slightly.

The room-temperature mechanical and engineering properties of thematerial in accordance with the present invention subsequent to heattreatment should be

yield strength R_(Po).2 : ≧590 N/mm²

tensile strength Rm: ≧850 N/mm²

break elongation A₅ : ≧16%

notch-impact work (ISO V section) A_(v) : ≧34 Nm

break tenacity K_(Ic) : ≧100 MNm^(-3/2).

Notch-impact work in the shallow A_(VH) level should be at least 65 Nmat a temperature that has not yet been determined.

We claim:
 1. High-strength solid wheels and tires of forged and rolledalloyed steel, quenched and tempered, for railroad traction vehicles andcars, said steel comprising, in percent by mass, of

    ______________________________________                                        carbon:        0.380-0.420                                                    silicon:       ≦0.250                                                  manganese:     0.400-0.600                                                    phosphorus:    ≦0.012                                                  sulfur:        ≦0.005                                                  chromium:      1.000-1.500                                                    molybdenum:    0.300-0.600                                                    nickel:        0.700-1.200                                                    aluminum:      0.015-0.040                                                    nitrogen       ≦0.008.                                                 ______________________________________                                    


2. Solid wheels and tires as defined in claim 1, wherein said steelcomprises further, in percent by mass, of

    ______________________________________                                        chromium:      1.00-1.30                                                      molybdenum:    0.30-0.50                                                      nickel:        0.70-1.00.                                                     ______________________________________                                    


3. A method of heat treating solid wheels and tires of the steel definedin claim 1 for total quenching and tempering comprising the stepsof:hardening at 850° to 900° C. followed by quenching in water or oil atroom temperature at approximately 20° C.;and annealing at 600° to 680°C. followed by slow cooling in air to room temperature at approximately20° C.